1. Field of the Invention
The present invention relates to a fuel cell formed by stacking an electrolyte electrode assembly and a separator in a stacking direction. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes. A passage extends through the fuel cell in the stacking direction for allowing at least a reactant gas or a coolant to flow in the stacking direction.
2. Description of the Related Art
For example, a polymer electrolyte fuel cell employs an electrolyte membrane (electrolyte). The electrolyte membrane is a polymer ion exchange membrane. A membrane electrode assembly includes an anode, a cathode, and the electrolyte membrane interposed between the anode and the cathode. Each of the anode and the cathode includes an electrode catalyst and porous carbon. The membrane electrode assembly and separators (bipolar plates) sandwiching the membrane electrode assembly make up a unit of a fuel cell (power generation cell) for generating electricity.
In the fuel cell, a flow field for allowing a fuel gas (hereinafter also referred to as the reactant gas) to flow along the anode is formed on a separator surface facing the anode, and a flow field for allowing the oxygen-containing gas (hereinafter also referred to as the reactant gas) to flow along the cathode is formed on a separator surface facing the cathode. Further, a flow field for allowing a coolant to flow between the separators is formed in each of the power generation cells, or in every predetermined number of the power generation cells.
In the structure, it is necessary to reliably seal the flow fields for preventing the fuel gas, the oxygen-containing gas, and the coolant from being mixed together, and preventing entry of foreign material into the flow fields, or short-circuiting between the separators. For this purpose, various sealing structures are adopted.
In the normal sealing structure, if the sealing material or the membrane electrode assembly is contracted due to the change in temperature, or deterioration over time in the stacking direction of the separators, gaps are formed between the separators and the sealing material. As a result, entry of foreign material, or degradation of the power generation performance or the like may occur easily. In an attempt to address the problem, in a known fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2002-305006, insulating members are provided around passages formed in separators.
Specifically, as shown in FIG. 5, the separators 1 and membrane electrode assemblies (not shown) are stacked alternately, and a passage 2 extends through the separators 1 in a stacking direction for allowing the reactant gas or the coolant to flow through the passage 2.
Each of the separators 1 is formed into one piece using stainless steel plate or the like. Sealing members 3 are formed integrally with the separators 1. Annular insulating members 4 are provided around the passage 2. In the structure, the insulating members 4 effectively prevent electrical short-circuiting between the separators 1 and degradation in the sealing performance due to entry of foreign material when spacing between the separators 1 is increased, or due to deterioration over time.
The seal height of the sealing member 3 in the stacking direction may be reduced over time. Thus, the insulating member 4 is compressed easily in the stacking direction. In the conventional technique, an inner edge la of the separator 1 around the passage 2 is provided in a range H where the adjacent insulating members 4 contact each other.
When the insulating member 4 is compressed, the metal inner edge la is not deformed elastically. Therefore, the elastic coefficient in the vicinity thereof becomes large. Thus, by the decrease in the compression load applied to the insulating member 4, the sealing line pressure (compression load per unit length of the seal) is reduced, and the sealing performance may be degraded undesirably. Further, an elastic deformation amount varies between a portion of the insulating member 4 where the inner edge la is present and the other portion of the insulating member 4. Therefore, the sealing performance may be degraded undesirably.